Technical Field
This disclosure concerns the implementation of distributed-antenna systems providing multiple services, such as cellular telephone voice and data, Wi-Fi, broadband internet service, low-power TV and others.
Background
The wireless local area network (WLAN) market is rapidly growing, and the variety of hotspots targeted for implementation is considerable. A “hotspot” is a physical location that offers Internet access over a WLAN through the use of a router connected to a link to an Internet service provider. Hotspots typically use Wi-Fi technology. Many of the hotspots targeted are large and achieving good coverage may be challenging. The current standard for providing coverage is to distribute individual WLAN access points (APs) in the target area. The number of APs needed by using this method may become significant. For example, up to 5000 APs can be required to provide coverage in a facility such as an airport. Today, it is estimated that 80% percent of all mobile voice and data connections occur indoor, so the problem of providing connection to WLAN and other services is only growing.
A distributed-antenna system (DAS) is the infrastructure used to distribute radio signals from one or more radio base stations and radio access points to any number of antennas located throughout the wanted coverage area. The coverage area may be covered by one or more cells, where each cell is typically served by any number of antennas multi-casting the same signal.
The DAS is the most effective and most flexible method to provide coverage inside a building. A DAS allows better control of the service area borders of the in-building system. At the same time, it provides high-quality coverage and low interference compared with using base stations and access points with integrated antennas. In addition, the DAS provides better radio trunking efficiency by allowing larger portions of the building to be served by a single cell or access point. This makes the frequency planning easier since fewer channels are needed to support the in-building traffic, which results in higher capacity with less interference.
An array of antennas distributed via a coaxial feeder network (passive DAS) is currently the most popular antenna configuration for cellular in-building solutions. The typical passive DAS comprises antennas, regenerators, power splitters and tappers, feeder cables, connectors and jumper cables. The disadvantage of a coaxial distributed-antenna network is that in a typical network, the coaxial cabling uses between 20 and 30 dB of the link budget. This results in the need of relatively high power at the base station antenna connector and the resulting high cost of the power amplifier. The possibly large cable loss puts also a limit to the WLAN deployment.
Radiating cable is an alternative to distributed-antennas in many applications, such as large apartment or office buildings or tunnels. A radiating cable (also called “leaky cable,” or “leaky feeder” in this disclosure) is a modified coaxial cable with slots in the outer conductor, which allows a controlled part of the RF signal to leak out of the cable, and also allows external RF signals to be coupled into the cable. In this disclosure, the terms “radiating cable”, “leaky cable”, or “leaky feeder” can also refer to any RF transmission medium now known or hereafter developed that is capable of efficiently radiating and receiving RF radiation with a coupling loss less than about 80 dB. Thus, the cable works as a continuous antenna and can be placed everywhere coverage is needed. Current distributed-antenna systems, with or without radiating cable, do not satisfactorily address problems of multi-band operations (e.g., cellular voice and data, Wi-Fi, HD TV, low-power TV, and public safety radio, among others) on the same antenna, problems with optimizing signal power in different bands, difficulties with filtering, and implementation of data networks that could allow individual subscriber access to speed control.
What is needed is a system that solves the problem of RF indoor coverage in a broad range of frequencies with the same distributed-antenna system. The solution should optimize both spectrum use and coverage of closed environments such as offices or apartment buildings. A desirable such system should comprise modules that can be pre-assembled and configured on-site to speed installation time and lower costs. The leaky cable of such a distributed-antenna system can be installed during new building construction, and data-controlled RF injection modules can be configured and installed as required, including accepting updates as new technologies offering new services evolve and thus “future proofed.”